These hybrid ring couplers are frequently constructed using microstrip conductor technology.
Further, however, high-frequency couplers are also known in which the degree of coupling is generally set via lines coupled on the end or longitudinal faces. For higher coupling levels, such as are required for a power splitter, these distances are often very small, or even so small that they can no longer be produced economically.
Thus, for example, a directional coupler is also known from U.S. Pat. No. 6,946,927 B2, which is constructed using suspended substrate technology. In other words, a coupling path using stripline technology is provided on one side of a substrate and is connected to two first and second terminals, also constructed using stripline technology, on the substrate. On the opposite side of the substrate, a second coupling path is further arranged, which leads to a third and fourth output or terminal. In a plan view, the two coupling paths are arranged so as to overlap at least in part.
A high-frequency coupler which is even further improved, in particular in the form of a narrow-band coupler or power splitter, is known for example from EP 1 867 003 B9. According to this publication, an improvement is also achieved by providing interdigital capacitors, which are each coupled between a coupling path and the earth, in the longitudinal direction of the two coupling paths.
The main drawbacks of the directional couplers using coplanar line technology relate inter alia to the required minimum distances between the conductor paths coupled on the longitudinal faces and to the coupling factor, which is thus also limited. Further, the coupling factor is highly tolerance-dependent (etching tolerances and fluctuations in the dielectric constant of the substrate material have a disadvantageous effect). Further, a coupler using coplanar line technology is non-optimal as regards dielectric losses.
An ideal separation of forward and backward waves is additionally only possible using directional couplers which permit propagation of TEM waves. Directional couplers using microstrip conductor or coplanar line technology do not make propagation of pure TEM waves possible. Therefore, directional couplers using coaxial line technology are used.
However, directional couplers or power splitters using coaxial line technology are of a relatively complex construction. Thus, in conventional directional couplers of this type, extremely precisely milled housings have to be manufactured, which have to have very different housing interior widths for the different stages of the coupler. Thus, the arrangement, in particular at the transition from one coupling stage to the next, is highly critical, since precise dimensions have to be adhered to here both as regards the coupling lines and as regards the distance from the inner housing walls. Even minimal deviations here can lead to relatively strongly altered electrical characteristic values.
A directional coupler largely similar to the described prior art is also known from EP 0 669 671 A1. It comprises two coupling paths, which each extend between two terminals on different paths. Each of the two coupling paths has a coupling portion, the two coupling paths extending mutually in parallel at a predetermined distance in the region of the respective single coupling portions thereof, so as to produce the desired coupling effect in this case.
An arrangement which is comparable in this regard is also known from U.S. Pat. No. 4,797,643. The special feature in this case is that two directional coupler arrangements which produce a coupling effect are arranged in a shared housing. The actual coupling path is formed by two coupling portions that extend perpendicularly at a distance from one another and belong to the two coupling paths.
After passing through an intermediate path approximately ten times as long as the coupling portion, the two coupling paths cross a second time. At this second crossing point, the two coupling paths likewise again extend at an equal distance from one another, and form the next two interacting coupling portions there.
JP 5-191113 discloses a directional coupler in which each coupling path has just one coupling portion between the respectively associated terminals thereof, which portion interacts with a corresponding coupling portion, extending in parallel therewith, of the second coupling path.
The prior publication MOHAMED M FAHMI: “Multilayer Multi-Section Broadband LCC Stripline Directional Couplers”, 1 Jun. 2007, XP031111873, describes a coupler device, specifically a directional coupler having four terminal ports. However, this is a stripline coupler which is fundamentally of a completely different construction from the above-described coaxial couplers, which have intercoupled signal lines accommodated in a housing which serves as an external conductor.
Against this background, the object of the present invention is to provide an improved directional coupler, in particular a 3 dB coupler, which is improved by comparison with conventional solutions in terms of costs, losses and manufacturing tolerances.
The object is achieved according to the invention in accordance with the features set out in claim 1. Advantageous embodiments of the invention are set out in the dependent claims.
The directional coupler according to the invention has major advantages over the prior art.
The directional coupler according to the invention is distinguished primarily by having a low tolerance-sensitivity whilst maintaining very good electrical values. In addition, the housing of the coupler according to the invention can be produced in a convenient manner. Overall, the coupler according to the invention is simple to manufacture and calibrate, making possible manufacture which is more cost-effective overall than conventional solutions.
The directional coupler according to the invention comprises a housing as an external conductor, which may preferably be manufactured as an injection-moulded part. Although injection-moulded parts of this type undergo or have to undergo subsequent machining in relation to the housing interior, the manufacture of an injection-moulded housing of this type is much more cost-effective than a housing which previously had to be milled in accordance with the prior art. The housings previously had to be milled because directional couplers of this type were highly tolerance-dependent, and the required precision could only be adhered to using a milled housing.
Further, the directional coupler according to the invention is distinguished in that the coupling portions of the two coupling paths of the multi-stage broadband directional coupler are defined with respect to one another by transition regions, which are also referred to as discontinuities for simplicity, even though the transition need not be exactly abrupt but rather takes place gradually over some distance. At these transition points, the coupling portions have an altered line cross section, i.e. the line thickness and/or line width thereof changes and/or the coupling distance changes, i.e. the distance between the two adjacent but galvanically separated coupling lines. Subsequently, capacitively acting shields are provided in the interior of the coupler housing in this region as a compensation device for the aforementioned transition regions.
In the context of the invention, it is thus ultimately also possible for the coupler housing to be able to have a more or less equal housing interior width over the coupling path or for this housing interior width only to vary relatively little over the length of the housing. In conventional multi-stage directional couplers, the housing interior width varies greatly in relation to the individual coupling portions. It was perfectly normal for the housing interior width to have to be configured 2 to 3 times larger from an initial coupling portion to a subsequent or central coupling portion. The interior ratios and dimensions still had to be adhered to extremely precisely, in particular at the transition regions from one coupling portion to the next.
In a preferred embodiment of the invention, it is further possible for the coupling distance, in particular between the coupling portions positioned closest together, to subsequently be able to be fine-tuned slightly by the possibility of inserting and/or fixing dielectric spacers (for example in the form of a plastics material plate etc.), which may be of small dimensions, between the coupling portions positioned closest together.
Also, one or the many further advantages in the context of the invention is that the coupler housing can be separated into two equal coupler housing halves along a separating plane. Each of the two coupler housing halves comprises one of the basically two coupling paths. Thus, each housing half can be mounted along with the associated coupling path, and subsequently the complete coupler housing can be finished by putting the two coupler housing halves together.
Further advantages, details and features of the invention can be seen in the following from the embodiment described by way of drawings, in which, in detail:
The multi-stage directional coupler shown in the drawings is formed for example as a 3 dB directional coupler. However, the coupling path may also be configured differently, in such a way that power splits other than 50:50 are also possible at any time.